Manure/Odor Control

Vertical Biofilter Uses Less Space, Provides Payback Horizontal biofilters are a proven technology when it comes to reducing odor and gas emissions from swine buildings. But that benefit comes at a price possibly requiring significant land area, depending on the amount of airflow from a building. Vertical biofilters, which place the media in a wall rather than lying flat, require a smaller land mass

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Vertical Biofilter Uses Less Space, Provides Payback

Horizontal biofilters are a proven technology when it comes to reducing odor and gas emissions from swine buildings. But that benefit comes at a price — possibly requiring significant land area, depending on the amount of airflow from a building.

Vertical biofilters, which place the media in a wall rather than lying flat, require a smaller land mass or footprint.

This research trial investigated design parameters for vertical biofilters in order to develop a more efficient system of dispersal of odor and gases from the building.

As the biofilter media settles in the vertical wall, it is denser at the bottom than at the top. This results in more airflow at the top and less airflow at the bottom.

To ensure uniform airflow at all points along the wall height after media settling, the design was modified to taper one side of the wall, resulting in a thicker top than bottom (see Figure 1).

Researchers studied which taper was required to achieve uniform airflow after 6 to 12 months of media settling. Three slopes were evaluated: 0 degrees, 4.8 degrees and 9.6 degrees. The 9.6-degree taper showed the least airflow variation across the biofilter media wall.

Media moisture is vital, as microorganisms in the media require moisture to maintain activity in breaking down the odorous compounds.

Two moisture application systems were tested. The first system placed a drip hose vertically through the media wall. The second system placed the drip hose on the top of the media wall, allowing the water to seep through the media. The second system provided a more evenly distributed media moisture content.

Dietary Manipulation Can Greatly Change Manure Composition

Reductions in nitrogen and phosphorus levels have little impact on swine growth performance. But the improvements have potential impact on waste treatment system designs, the amount of land needed for effluent application and possibly gaseous emissions.

Two experiments evaluated the role of dietary manipulation on nutrient excretion of group-housed pigs during a 112-day finishing period.

In each trial, 48, 65-lb. pigs were placed on two diets. Each test diet was a low-protein, low-phosphorus ration supplemented with amino acids. In both experiments, a typical corn-soybean meal diet served as the control diet.

Dietary crude protein was reduced in Trials 1 and 2 by 2 and 4%, respectively. In both experiments, dietary phosphorus declined 0.10%. All diets were similar in lysine content.

While diets had no effect on growth, the impact on nutrient excretion was pronounced. Reducing dietary crude protein by 2% reduced the concentration of nitrogen and ammonium nitrogen in manure by 18 and 26%, respectively.

When dietary crude protein was cut by 4%, nitrogen and ammonium nitrogen levels in manure dropped by 40 and 55%, respectively.

The 0.10% drop in phosphorus content of the diet reduced the phosphorus levels in manure by 22%. The pH levels in manure were also reduced with the 4% drop in dietary crude protein.

Daily dry matter excretion was not affected by dietary manipulation in either experiment. But reducing dietary crude protein levels by 2 and 4% reduced daily nitrogen excretion by 20 and 40%, respectively (Figure 1 on page 18). Phosphorus excretion was cut by 25% by lowering the dietary phosphorus content.

These daily reductions in pig excretion levels of nutrients represented a cumulative decrease of 1.68 and 3.01 lb. of nitrogen when crude protein levels were decreased by 2 and 4%, respectively. Cumulative excretion of phosphorus was reduced by 0.34 lb./finishing pig. Potassium and iron levels also decreased.

Diet cost in the trials, supported by USDA and Pork Checkoff funding, is certainly an issue. Lowering the crude protein content by 2% with addition of lysine is cost-effective, while a diet producing a 4% reduction of nutrient excretion may not be cost-effective.

However, the marked reduction in nitrogen and phosphorus excretion could possibly offset any increase in diet costs, particularly as environmental regulations tighten.

Reduced Trace Minerals Lower Excretion Rates

By feeding lower levels or organic forms of copper, iron and zinc to grow-finish pigs, soil nutrient buildup is minimized and potential toxicity to plant growth, grazing animals and aquatic species through soil erosion and water runoff are avoided.

Feeding lower levels of trace minerals also reduces consumer pressure. The European Union has already banned high inclusion rates of copper, iron and zinc in swine diets. Producers in the United States should expect to see similar legislation in the future.

Trials conducted at Iowa State University (ISU) evaluated two levels of inorganic and two levels of organic trace minerals. All organic materials tested were courtesy of Alltech Inc. (Bioplex), Nicholasville, KY.

Pit Fans May Prove Unnecessary in Deep-Pit Manure Storage

For indoor air quality, the data shows limited benefit to exhausting a portion of the air through the pits rather than through the walls, according to University of Minnesota bioproducts and biosystems engineering professor and project coordinator Larry Jacobson.

That finding allows pork producers to “strategically decide to use just wall fans for their deep-pit barns, or if emissions of odor or gases are of concern, to utilize limited pit fans that have control technologies (such as biofilters) to substantially lower those emissions from the barn,” he suggests.

Research results were drawn from a 2,400-head, double-wide finishing building, studying just the western 1,200-head room of the barn. That room featured four, 24-in.-diameter pit fans operated in two-hour intervals at 0, 4, 10 and 20 cfm/pig ventilation rates. A 36-in. wall fan was set to operate continuously, but restricted to an airflow rate of 4,000 cfm. The other four, 50-in.-diameter wall fans were operated as needed by the room's ventilation controller.

Air was sampled in the middle of the barn to measure indoor air quality, at the fan end of the barn for a second indoor air quality measurement and also for wall emission calculations.

Data collection started in the fall of 2005 and finished in July 2006. The data covered two different pig groups and was divided into winter, spring and summer categories. Preliminary results showed:

The indoor air quality, which is represented by the ammonia and hydrogen sulfide concentrations, are depicted for the spring season in Figures 1 and 2, respectively, on page 23. The small differences in the ammonia and hydrogen sulfide concentrations at the different pit ventilation rates indicate that the operation of pit fans have little impact on indoor air quality.

This trend is similar for the winter and summer seasons, with only the absolute value of the gas concentrations being higher in winter and lower in summer.

“When there was reduced or no pit ventilation, the temperature-controlled wall fans were activated and effectively kept the barn's total air exchange rate relatively constant over the four ventilation treatments,” explains Jacobson.

Relatively constant indoor concentrations of carbon dioxide, shown in Figure 3, also reflect the lack of impact of pit ventilation.

Emission rates for ammonia and hydrogen sulfide show that for both gases, the total building emission remains relatively flat for the different pit ventilation rates. The wall emissions for both gases consistently decrease as additional pit ventilation was added.

Pit and wall emission rates are similar in magnitude for both gases at the 10 cfm/pig pit ventilation rate.

Results from all three seasons for particulate matter under 10 microns indicates that for almost all pit ventilation rates, less dust was emitted from pit fans than from wall fans.

Odor emission results for all three seasons showed that when pit ventilation was provided, as much or more odor was emitted through the pit as was emitted through the wall fans, even though the pit ventilation represented only 10 or 20% of the total ventilation airflow through the barn.

Based on these findings, if a producer decides not to use pit fans in the barn's ventilation system design (or only use one or two fans), then capital and operating costs for the ventilation systems can probably be cut 10 to 20%, as larger, more efficient wall fans replace smaller pit fans.

If a producer wants to focus on reducing the air emissions from a barn, treating just the exhausted air from a limited number of pit fans would be a cost-effective way to achieve a sizeable (up to 50%) reduction in odor or gas emissions, depending on the control technology.